For a vehicle without suspension to move over a rough surface, the whole vehicle must rise and fall over every bump. The faster the vehicle moves, the more rapid becomes this up-and-down motion. Bumps hit at high speed can push the vehicle up very hard, but cannot fall back any faster than gravity pulls it. Therefore, even at moderate speeds, the wheel can leave the ground over the top of bumps. A wheel in the air cannot give any grip.
Technology can provide a considerable amount of power, but it is useless unless the tyres are kept in firm contact with the road. Modern vehicle suspensions, acting with the pneumatic tyres, isolate the vehicle, driver and load from these vertical forces. They control the vertical oscillations, caused by traversing uneven terrain or performing rapid manoeuvres such as accelerating, braking or cornering.
Known suspension systems are often a compromise, as they aim to fulfil two opposing functions:    a) Driving comfort, by protecting the driver and loads from vertical oscillations. This is typically achieved by using low spring characteristics such as those found in many luxury motor cars. They commonly have a static to bump spring ratio of about 3:1, tend to be long wheel based and require stiff anti-roll bars to counter the inherent low handling dynamics.    b) Safe vehicle handling dynamics while performing rapid vehicle manoeuvres. This is typically achieved by using a high spring characteristics, as found in most sports/racing vehicles. They commonly have a static to bump spring ratio of about 5:1, but in some cases can be over 9:1. The ratio is limited by the driver's discomfort.
The compromise being: improving driving comfort reduces the dynamic handling; while, improving dynamic handling reduces driving comfort.
This matter is further complicated by the fact that safe handling dynamics can be quantified, but driving comfort cannot. Driving comfort is a personal feeling, each person's tolerance and thresholds are different as they are the result of many factors including involving human senses.
Designing suspension systems for the everyday vehicle is not usually an arduous task, as the levels of comfort to dynamic handling tend to be within reasonable limits and not at extremes. Problems arise when those levels do reach extremes, eg for off-road or sports/racing vehicles, and is where the handling dynamics become limited by the individual driver's discomfort (fatigue).
Suspension systems are generally formulated by applying proven mathematical models and using known technologies to produce a solution with defined compromises. This is achieved as the spring and damping characteristics are a direct resultant of:    i. The range of mass being supported by each wheel, ie from unladen to fully laden (vehicle dependant).    ii. The appropriate vertical wheel travel (terrain dependant).    iii. The speed traversing over the terrain (driver comfort dependant).    iv. The vehicle classification, eg luxury, road, sport or race (driver comfort/vehicle handling dynamics dependant).
Compensating for this need to compromise has led to the necessity to incorporate auxiliary suspension stabilizers, such as anti-roll bars (or ‘sway bars’) which restrict axle articulation. The relentless quest to provide reasonable driving comfort along with good dynamic handling has also led to the generation of a wide variety of suspension geometries aimed at limiting the vertical body movement while reducing pitch and roll.
Most known suspension systems are essentially non-adjustable. Some bespoke suspension systems for racing vehicles allow some form of limited adjustment. Such adjustments are currently limited to:    a) Ride height via mechanical mechanisms (for example by way of a threaded spring stop on over-coil shock absorber).    b) Low flow rate bump damping by way of needle valves to independently adjust the low flow rate damping force generated during bump (wheel rising, also known as ‘Jounce’ in USA).    c) Low flow rate rebound damping, also by way of needle valves to independently adjust the low flow rate-damping force generated during rebound (wheel lowering).    d) High flow rate bump damping is only available to the professional racer.    e) High flow rate rebound damping is usually only available to the professional racer.
Although these bump and rebound adjustments a) and b) principally affect the low flow rate damping forces, they also change the high flow rate characteristics by very small amounts.
The slope and shape of the high flow rate characteristics are defined by, and changed by, damping washers or ‘shims’. These however can only be changed by a specialist (eg the manufacturer or its authorised dealers) and is not an adjustment that can be made by the driver.
It is to be noted that the modern racing shock absorber tends to be front or rear wheel specific for a defined vehicle, and cannot be moved from front to rear wheel of the same vehicle, let alone from one vehicle to another.
Air and hydro-pneumatic suspension systems regulate the vehicle's ride height by adjusting:    i. The air pressure, for vehicles such as HGVs, Range Rover, Mercedes Benz, Rolls Royce or Harley Davidson. Changing the air pressure with the same chamber volume alters the spring stiffness. However, the static to bump spring characteristic tends to be linear, remaining the same in relation to the charge pressure (around 3:1). This type of system uses rubber air bags which are limited to a maximum working pressure of about 100 psi, and tend to be large in diameter (as force=pressure×area) and are easily damage by road debris. They also need auxiliary equipment such as compressor pumps, accumulators, valves, fixed and flexible pipework to function. This limits the working medium to air, requiring the necessity of eliminating the ingress of moisture (causing rust and hydraulic lock).    ii. The volume of hydraulic fluid, for vehicles such as Citroen. Adjusting the oil volume to compensate for the change in gas volume does alter the vehicles height, but does not affect the spring characteristics.
We have realised that it would be highly desirable to provide a suspension assembly which is readily adjustable so as to suit a specific track or circuit, weather conditions, the weight of the vehicle (from unladen to fully laden) and the driver's racing style.
In a highly preferred embodiment of the invention a suspension assembly includes the following adjustable features:    a) The ability to produce either near-linear or true non-linear spring characteristics.    b) The ability to set or adjust the static to bump spring rate anywhere from below 3:1 to over 9:1.    c) The ability to control the rate of change in spring rise, either gradual or abrupt.
In a further embodiment of the invention a suspension assembly includes the feature of dynamic roll control. Fitted to each the steered wheels, two such assemblies can be interlinked to reduce or induce dynamic roll control during cornering. The spring characteristics and ride height of the suspension assemblies connected to the steered wheels are automatically caused to change during cornering to reduce or induce body roll control, resulting in improvements to the dynamic handling of the vehicle.
In yet a further preferred embodiment a suspension assembly is fitted to each wheel station and the suspension assemblies are interlinked to improve safe vehicle handling dynamics, while performing rapid vehicle manoeuvres ie accelerating, braking and cornering etc. This advantageously provides automatic dynamic pitch and roll control.
The pitch and roll control arrangement mentioned above differs from the dynamic roll control arrangement in that it affects the suspension assemblies on all wheel stations to redistribute the forces generated during vehicle manoeuvring to alter the spring characteristics and ride height which in turn reduces body pitch and roll, resulting in improved dynamic handling of the vehicle.
The suspension assembly mentioned above preferably allows control of the vehicle's attitude, along with the ability to lower the overall centre of gravity during vehicle manoeuvring, allowing the vehicle to traverse through corners faster. In use adjustable features preferably allow for:    a) Coarse changes to the static to bump spring characteristics, enabling adjustments to suit ‘road/track’ or ‘road/off-road’ and vice-versa, eg from below 3:1 to over 9:1.    b) Fine changes to the static to bump spring characteristics allow the suspension to be fine tuned to suit changes in:            i. The vehicle mass, from unladen to fully laden.        ii. The centre of gravity.        iii. Personal driving techniques.        iv. Track-to-track conditions, etc.        
The suspension assembly can preferably be installed into any vehicle to provide variable suspension parameters, eg on the everyday car, motorcycles, sports cars and bespoke high performance vehicles.
Adjustment of the spring rate may be likened to adjusting the headlamps in most everyday cars. The headlamps are re-aligned to compensate for the change in weight of the vehicle, caused by passenger(s) and/or luggage. A similar control arrangement could be used to dynamically change the spring characteristic and restore the vehicles' comfort and handling dynamics back to an acceptable level or to change the spring characteristic from comfort-to-sports mode or from one sports mode to another. Such a control feature would ideally suit motorcycles, as the comfort/driving dynamics varies greatly from unladen to fully laden. It would also allow sport cars and high performance vehicles comfort and handling dynamics to be set for ‘road/track’ or ‘road/off-road’ or ‘road/track/off-road’ use.
To achieve the new features and options, the new suspension unit preferably incorporates two forms of novel technologies:    1) The separation of the damping valves away from the piston.    2) The introduction of a floating damper plate.
Relocating the valves away from the piston increases the applied forces generated by the compressed gas. This additional force is used to create the non-linear static to bump spring characteristic. The change also increases the oil flow rate through the damping valves, resulting in producing greater damping forces.
The floating shock absorber plate enables the high flow rate bump and rebound damping forces to be easily adjusted.
As the suspension systems are a compromise between driver comfort and handling dynamics, there is a well-established large world-wide market for those who want to modify their vehicles suspension system for street, track, circuit or competition use. They range from the basic amateur and DIY enthusiast, through to the true international professional racing teams, all looking for the ultimate in driving performance.
Currently, changing the compromise for mass produced vehicles involves physically changing the existing springs and shock absorbers. They tend to fall into the following four categories:    a) Retain the existing springs, but change to stiffer or adjustable shock absorbers—thus giving a slightly less comfortable ride but improved handling. This setup is typical for street use.    b) Change to stiffer springs and adjustable shock absorbers, this is usually coupled with lowering the ride height by around 25/40 mm, fitting stiffer anti-roll bars and low profile tyres—thus giving far less comfortable ride but much improved handling. Various levels of this setup are typical for street, track, circuit and competition racing.    c) Change the springs for air suspension, this results in a softer ride with the ability to adjust or maintain the ride height (self-levelling)—thus giving a softer more comfortable ride than standard, but with reduced dynamic handling. This setup is typical for the luxury vehicles, street use or as booster springs for self-levelling the rear axles of pick-ups and light trucks.    d) Change the springs and shock absorbers for a hydro-pneumatic suspension system, this allows dynamic movements to the vehicle—this often gives a slightly softer more comfortable ride than standard, along with a slight reduction in dynamic handling. This setup is also typical for street use.
It is noted that option (c) is becoming a common solution as it does allow adjustment to ride height along with self-levelling. It also has the ability to maintain a constant static to bump ratio relative to a variable static wheel load. However, it does require auxiliary equipment and power to perform these features.
Whatever the category of suspension type, the results tend to be limited as they render the vehicle specific for use, eg it can only be used in one category, and only allows limited adjustment within that category.
Furthermore, the existing replacement shock absorbers need to have their damping valves ‘sized’ to suit specific wheel loading. Some shock absorbers are even vehicle make and model specific, ie Audi TT or Honda S2000, and have limited independent adjustment for bump and rebound. If the vehicle changes its parameters too much (wheel loadings due to weigh reduction), the damping valves need to be re-sizing.
Thus if it is desired to alter the suspension settings from say road use to track use this cannot readily be achieved since known suspension assemblies only allow changes to the shock absorber low flow rate bump and rebound settings only. Changing the static to bump spring characteristics, to suit from road to track and vice-versa, let alone changing the spring characteristics from track to track, are none existent.
FIG. 1 shows a typical modern vehicle's over-coil shock absorber assembly. It comprises of a coil spring with a shock absorber in the middle. The shock absorber can be supplied in a single-tube or twin-tube design, both using the same technologies for body motion control and system damping. Such typical single-tube type shock absorber assemblies are supplied by Ohlins, Bilstein, Monroe or Koni.
One end of the shock absorber assembly is attached to the body of the vehicle while the other end is attached to the axle. A coil spring is contained between flanges on the con-rod and the cylinder. The vehicle's vertical movement causes the con-rod to move inside the cylinder. This movement results in:    a) Compressing or extending the coil spring, storing or releasing the energy within the coil spring to provide vehicle body motion control.    b) The piston and valve assembly moves inside the cylinder, forcing oil through the valve assembly, providing the damping forces that keep the tyre in contact with the road.
A separator piston and nitrogen gas compensate for the differences in oil volume needed from one side of the piston to the other. The system is pressurised, between 12-30 bar, to stop the oil aerating and cavitating while under dynamic conditions.
As the pressurised oil acts on both sides of the piston, its working area is limited to the difference between the two areas, ie the con rod diameter. The gas pressure acting on this small area is still sufficient to cause the shock absorber to fully open when removed from the vehicle.
The coil spring provides the vast majority of the supporting forces for the suspension system with only a residual force provided by the Nitrogen gas. Coil springs tend to be linear in their static to bump spring characteristics. Non-linear spring characteristics are available, by:    i. Tapering the spring material diameter.    ii. Varying the pitch of the coils.    iii. Varying the radius of the coils.    iv. Stacking different rated springs, one on top of the other.
Either way, the amount of non-linearity is limited in scope, along with the associated static to bump spring characteristics, primarily due to spring binding (coils touching).
Coil springs suffer from a major problem, once manufactured it is very difficult to change the static to bump spring characteristics. This can only be achieved by physically changing the spring's parameters, such as:
The mechanical properties of the material.
The coil diameter.
The coil radius.
The coil pitch.
Changing one spring for another with a different spring characteristic.
The piston has a ring of two sets of holes through it, allowing oil to flow from the outer edge of one side to the inside of the other side. For each side of the Piston, the inner holes are covered by a thin washer which is held against the Piston by either its inner or outer edge, with the other edge free. Stacked on top of these washers may be other washers or spacers to modify its stiffness. One stack of washers are used during bump damping and another stack are used during rebound damping.
At a low rate of flow, the bump damping forces are generated by the oil being forced through a by-pass hole, as illustrated at item 3 in FIG. 2. The oil pressure developed is not sufficient to deflect the washer, at the bottom of the piston, to allow oil to flow through the apertures in the piston.
At a higher rates of flow, such as when the vehicle is driven over a bump, the oil pressure developed pushes against the washer with sufficient force to be deflect it into a slightly conical form. This allows oil to pass through the low flow rate orifice and the damping holes and out from under the deflected edge of the washer, as illustrated at items 2 and 3 in FIG. 2. The washer can be likened to a kind of stiff reed valve, made in circular geometry. The faster the piston moves, the more the washer stack deflects increasing the orifice area.
When the mass of the wheel and the coil spring forces the shock absorber to extend again, during rebound, the oil flows in the opposite direction, as illustrated in FIG. 3. It uses the same low flow rate by-pass damping but uses the washers on top of the piston and not the bottom ones.
The characteristics of the damping forces can be changed by altering the size of the washers (the number, thickness and diameter). Therefore, changing the washer stacks on either side of the Piston allows different bump and rebound damping force characteristics to be used. However, this can only be done by the shock absorber manufacturer's authorized service workshops.
The initial adjustable shock absorbers utilise a needle valve located in the centre of the piston, as illustrated at item 3 in FIGS. 2 and 3. This allows for adjustment of the low flow rate for bump and rebound. This adjustment is only used for low-speed motion control, ie to prevent wallowing. The adjustment also alters the higher speed damping generated by the damping valves a little.
Using the same adjustment for low flow rate bump and rebound damping causes a dilemma, too much damping, to prevent wallowing, induces hopping and wobbling. To stop this hopping and wobbling, the ideal setup is to have the bump damping forces about 20%-25% of the rebound damping required to prevent wallowing.
This requirement has led to some shock absorbers having independent bump and rebound damping forces adjustment. Again, these adjusters only act on the low oil flow rate only and are used to adjust low-speed motion control. The adjustment still alters the associated higher speed bump and rebound damping forces generated by the damping valves a little.
In summary it can be seen that known over-coil shock absorbers comprise a coil spring to support the mass of the vehicle and comprise a shock absorber to generate the forces required to reduce the vehicle oscillations. These units rely on adjusting the damping forces only to compensate for the compromise between driver comfort and handling dynamics.